WEDNESDAY, Aug. 8 (HealthDay News) -- As thousands of elite athletes gather in London to make their respective runs for gold, a new study suggests they face a higher risk of becoming ill if they travel across more than five time zones to get to a competition than if they compete at home.

The researchers studied the health of more than 250 high-level rugby players who took part in a 16-week tournament in three countries during 2010. The teams were from Australia, South Africa and New Zealand, and they went to places that were at least two time zones from their own (and as many as 11).

More than 72 percent of them reported illnesses, and they were sick 21 out of every 1,000 player days.

Those who played at home before going abroad had an illness rate of 15.4 for every 1,000 player days, but the rate grew to 32.6 in places whose time zones were five or more hours away from the players' homes. It didn't matter in which direction the athletes traveled.

When the players got back home after being abroad, their illness rate fell to 10.6 per 1,000 player days.

About a third of illnesses were respiratory problems, followed by gut conditions (28 percent) and skin and soft tissue disorders (23 percent). Most of the illnesses were due to infections.

Could air travel itself account for the health issues? The researchers don't think so, since the illness rates dropped when the players got home.

"The results from our study indicate that the illness risk is not directly related to the travel itself, but rather the arrival and location of the team at a distant destination," the authors wrote.

Potential causes could include pollution, the aggravation of allergies, exposure to different foods and germs, and changes in temperature, humidity and altitude.